Airplane structure



May 10, 1938.

A. sAMB Aus' AIRPLANE STRUCTURE Filed Sept. 7, 1934 Adof; a, g .F

awn/or Attorney May 10, 1938. A. SAMBRAUS AIRPLANE STRUCTURE Filed Sept. 7, 1934 6 Sheets-Sheet 2 May 10, 1938.

SAMBRAUSQ I 2,116,953

AIRPLANE STRUCTURE May 10, 1938. A. SAMBRAUS 2,

AIRPLANE STRUCTURE v Filed Sept. 7, 1934 6 Sheets-Sheet 4 k jww May 10, 1938. A. SAMBRAUS AIRPLANE STRUCTURE 6 Shets-Sheet 5 Filed Sept. 7, 1934 y 1938. A. SAMBRAUS 2,116,953

AIRPLANE STRUCTURE Filed Sept. '7, 1934 6 Sheets-Sheet 6 l B] 4402i??? rm WATlol-wey Patented May 10, 1938 PATENT OFFICE AIRPLANE STRUCTURE Adolf Sambraus, Berlin-Charlottenburg, Germany Application September 7, 1934, Serial No. 743,126

3 Claims.

My invention relates to airplane structures.

It is an object of my invention to provide an improved airplane structure.

To this end, I make the structure, for instance,

5 the spars, ribs and other members of an airplane, as well as its covering, of thin sheet metal which has been treated for high quality, for instance, heat-treated. The parts of the structure including the covering are connected by a solder whose working temperature is such as to be without deleterious effect on the sheet metal.

The term solder includes brazing solders as well as soft or lead-tin solder, and the upper limit of its working temperature is governed by the condition that the sheet metal must not be deteriorated. Obviously, the limit is determined by the chemical and mechanical properties of the sheet metal.

Continuous members for force transmission, with thin sections, for airplane constructions, are made of tubes, rolled sections or sheets of light metal or light alloy, or steel, and are connected by rivets and/or screws, and, in the case of steel, also by autogenous or electric spot welding.

In airplane construction, it has already been proposed to connect members of the fuselage and wing structure, and particularly the knots or such structure, by spot welding, as described in the U. S. patents to Rapp et al., 1,403,444, "Airplane wing construction, Jan. 10, 1922, and to Ragsdale, 1,880,481, Aircraft construction and making same, Oct. 4, 1932. It has aso been proposed to weld a covering of thin flexible steel to the ribs of an airplane structure, as described ;5 in the U. S. patent to Toman, 1,164,634, "Aeroplane, Dec. 21, 1915.

, Normal steel sheets are welded successfully if thick enough.

In the construction of machinery, it is old to [0 connect any parts, especially iron parts of thick section, by soldering or brazing.

According to my invention, the several members of an'airplane structure, such as the covering, the fuselage,-the wings and the rudders and i5 elevators of an airplane, are made of thin metal of foil-like thickness, for instance steel, to which high quality has been imparted by suitable treatment, and the parts of the members are connected by soldering.

50 such as the frames of the fuselage, the ribs of the wings and the corresponding spars, are connected at their intersecting points by soldering.

Any solder may be used whose working temperature is so low as not to deteriorate the sheet 55 metal at all, or not to an appreciable extent.

Continuous structural members Preferably the members are .tinned at the joints, or coated with cadmium.

Members subjected tocompression stress may be equipped with suitable bracing means, such as angular or closed sections, which are soldered 5 to the members without difliculty, as will be described below with reference to the drawings.

In the construction of machinery, there is a prejudice against soft soldering. However, I have found that in aircraft construction, if properly performed, soft soldering is surprisingly useful, particularly for long parts of thin sheet metal which has been treated for improving its properties. The term soft solder as employed here, includes solders whose melting point is intermediate between that of brazing solder proper, and soft orlead-tin solder. It is not necessary, that solder of the same working temperature should be used for all connections but solder of various working temperature may be used in the same structure, providing the working temperatures are within the limit defined above. Overlapped joints obtained with a solder of this type are much superior in strength to riveted joints in dural or steel. Under the most favorable conditions, the

load transmitted by a rivetedjoint is 2.5 kilogrammes per sq. millimetre of the overlapped area. Normally, it is only .8 kilogramme per sq. millimetre.

In a soldered joint which should have the same strength as the sheet metal, of steel whose tensile strength is '200 kilogrammes per sq. millimetre (such steel could not be used in aircraft structures if welded or riveted) and with a solder whose shearing strength is 3 kilogrammes per sq. millimetre, the length of the overlap should be equal to 6'7 times the thickness of the sheet metal. This size of the overlap is practicable under all normal conditions.

Soldering with a solder as defined above with 40 respect to its working temperature, is superior to welding in that the soldered overlap may be of any desired size, and any desired strength of the soldered joint may therefore be obtained.

Long and thin sheets of high-class materials as described are so flexible that the force to be transmitted through the joint is in the soldered face of the joint, and normal stresses which might damage the joint, are eliminated. The softness and ductility of soldered joints equalize stresses as against the stress-localizing effect of rivets and welds, and this is why such joints are particularly suitable for peak loads of short duration and alternating loads which occur so ire quently in aircraft structures.

For sheets of high-class material, soldering is the best connection as it does not involve alterations in the microstructure of the material and eliminates notching effects. Welding and brazing proper (see supra) make unreliable joints in such material because the high temperature is deleterious, and spot welding has the additional drawback of notching effect. This effect is also present in riveted joints and, as stated above, their strength is limited.

Soldering as against riveting may be compared to the universally adopted method of gluing in the construction of wooden airplanes which has superseded the tenon joint notwithstanding the low strength of the glued joint.

Thorough investigation has confirmed that in fact soldering is superior to riveting and welding for thin sheet metal.

The saving in weight of soldering as against welding amounts at least to as soldering permits the use 1 sheet metal of foil-like thickness which is asIthin as required by calculation, say, .02 millime welded.

Another point of superiority of soldering over welding and riveting is that as soldering is performed from the outside, members or parts which are difllcultly accessible can be connected by soldering without any difliculty, and still another point is that soldered aircraft, and particularly airplanes, are made without extra equipment and without skilled labor, and that at a faster rate than with the old methods of manufacture, because marking and drilling of rivet holes are dispensed with, subsequent heat treatment of finished steel aircraft is not required, and it is not necessary to wait until the glue has become dry, as in wooden aircraft.

The use of pressed and drop-forged standard parts is much facilitated and such parts do not require expensive dies, as forms which are favorable aerodynamically, strong and light, are obtained by wrapping and folding the thin sheet metal, as will be described with reference to the drawings.

Soldering is not only superior to welding and riveting as to the manufacture, but also as to the repair of aircraft. Repairs are made outside landing stations and repair shops by unskilled labor and with no other equipment than soldering irons. In the field, damaged parts of airplanes may be detached and replaced by parts of destroyed airplanes, and it is even possible to use e, and could obviously not be pieces of tin, for instance, tin cans, in such cases.

.ing end of a lattice-work wing rib as shown at "(1 in Fig. 1,

Fig. 3 is a perspective illustration of thetrailing end of a solid wing rib as shown at b in Fig. 1,

Fig. 4 is a perspective illustration of a modified lattice-work rib as shown at "c in Fig. l,

Fig. 5 is a perspective illustration showing the rear end of a fuselage equipped with three spars,

as at d in Fig. 1,

Fig. 6 is a perspective illustration showing the 'are all designated by the numeral 3.

rear end of a fuselage with spars distributed all over its cross section, as at "e in Fig. 1,

Fig. 7 shows a folded, and

Fig. 8 shows a wrapped portion of the fuselage, as at "f and "g, respectively, in Fig. 1,

Figs. 9a, 90 and 9e are plan views. of three kinds of joints for the covering, and Figs. 9b, 9d, and 9) are side elevations, respectively, of Figs. 9a, 90, and 96,

Fig. 10 is a diagram of the bending moments occurring in an overlapped joint,

Fig. 11 is a cross section of the upper portion of the rear spar in Fig. 4, at "i,

Figs. 12 and 13 are sections on the corresponding lines in Fig. 11, respectively,

Fig. 14 is a cross section of the fuselage structure illustrated in Fig. 5,

Fig. 15 is a perspective illustration showing one of the knots of Fig. 5, positioned at is,

Fig. 16 is a perspective illustration of one of the gusset plates in Figs. 14' and 15,

Fig. 17 shows bracing members positioned at m on the rear spar in Fig. 4,

Fig. 18 is a cross section similar to Fig. 11, showing bracing members at the sides of the upper flange of the rear spar, and

Figs. 19 to illustrate various sections of built-up structure members.

Referring now to the drawings, and first to Fig.

1, the fuselage l is equipped with wings 2, the wings are equipped with ailerons, and the rear end of the fuselage supports the usual rudder and elevators. The ailerons, rudder, and elevators The covering of the wings, Figs. 11 to 13, and the covering of the fuselage, Figs. 5 and 6, are formed by strips of sheet metal of the kind described. The strips, if of sheet steel, may be of foil-like thickness and as thin as .02 millimetre. Their joints are tinned or coated with cadmium, as described above, overlapped or strapped, and connected by a solder of the kind described whose working temperature has no deleterious effect on the sheet metal. I The members of the structure will now be described. Referring flrst to Fig. 2, this shows the front portion'of a rib 5 whose position is indicated at a in Fig. 1. The frame of the rib which is braced by filler strips 19 and vertical struts 2i in the manner of lattice work, is hollow and of square section. The struts are shown as angle sections by way of example. The frame, the filler strips and the struts are made of the thin sheet metal described, and connected by soldering, as'also described. 20 are covering stringers of hollow square section which are connected to the frame of the rib 5 by soldered gusset plates 22.

The wings have each a pair of spars, both .designated by the reference numeral4. The front spar is a box girder with side plates 21 and channel sections 28 at the top and bottom, all of the said thin sheet metal, and connected by the said solder, and braces 29 are soldered to the side plates 21. The rear spar is shown in Fig. 3 for a modified rib which has a solid body 24 soldered to its frame, braces 2| which correspond to the struts 2| in Fig. 2 and are soldered to the body or plate 24, and a trailing frame member 30 soldered to its rear end. The rear spar has a plate body 26 which intersects the rib body 24. The body of the rear spar is equipped with a strap 22 at the top and at the bottom, as shown for the top strap in Fig. 11. This figure illustrates the structure for a rib whose frame-is of open channel Section, as will be described with reference to 7 flowing of the heated solder.

- of open channel section, as mentioned, and

Fig. 4, but otherwise the design is the same as for the ribs in Fig. 2 and Fig. 3. Referring to Fig. 11, the strap 33 is connected to the plate body 26 by angle sections 34 at opposite sides of the body which are soldered to the body and the strap, and preferably have perforations 34a to facilitate the The perforations are filled with solder and also serve for ascertaining that the soldering operation has been properly performed. Triangular gusset stays 25 whose outer edges may be folded over for bracing are soldered to the sides of the rib frame and of braces 29 at opposite sides of the spar plate 26. Four gusset stays and two braces make up the connection, as shown in Fig.3.

The covering 35 is soldered to the frames of the several ribs which is facilitated by flanges on the frames, Fig. 12. It may also be soldered directly to the straps but preferably strips 22 are interposed for distributing and equalizing the forces. tothe vertical flanges of angles 34, and to the braces 29, as shown in Fig. 3, and may also be soldered to both flanges of 34 and to the corresponding gusset stays 25.

Referring now to Fig. 4, this rib has a frame shown in Fig. 12, and the covering stringers are also open sections. This rib is of lattice work and its lattice bars are partly diagonals and partly vertical struts, both marked 32. Their ends are connected to the plates 23 of the covering stringers, or to the gusset stays at the rear spar, by soldering.

The rear spar 26 is designed as shown in Fig. 3, but the front spar is a lattice-work girder, with straps 3| at the top and bottom, and struts and diagonals 3| between the straps, all of channel section and connected by soldering. "i is the portion which is shown to a larger scale in Fig. 11.

It is understood that Iam not limited to any one of the combinations illustrated, for instance, to the combination of' a box-girder front'spar with a rib of the type illustrated in Fig. 2, or to the combination of a plate rib with a plate rear spar, Fig. 3, etc., but may combine the several members as I may desire, without departing from my invention.

It will appear that soldering is performed without difliculty and without extra equipment, even for complicated connections such as shown in Fig. 11, without local heating and deterioration of the metal as are inevitable in welding. The operations are all performed with simple soldering irons. I

If desired, the straps 33 may be braced at the sides by soldering thereto bracing members which, as shown in Fig. 17, may be of V section with outwardly or inwardly extending flanges 31, or may be channel sections, as shown in Fig. 18.

Referring now to Figs. 5, 14, 15, and 16, these illustrate a fuselage in which the covering does not transmit forces but in which the covering Ml of the fuselage is connected to the fuselage structure by extra frames, not shown. By way of example, three fuselage spars i are illustrated making up a structure of triangular cross section, but I might also provide four or more spars in any polygonal arrangement. 6 are frames and are diagonals connecting them. Gusset plates 42, 43, and 44 are soldered to the spars d and the frames 6 and diagonals ll are also soldered to the gusset plates. I may provide separate gusset plates 42, as shown at the right in Angle sections are preferably soldered Fig. 14, or I may combine two gusset plates into an angle plate, as shown at the left in Fig. 14. This angle plate is connected by soldering to the corresponding spar 4, to two members of the frame 6, and to diagonals 4l.

Fig. 15 shows the portion at k in Fig. 5, drawn to a larger scale, and Fig. 16 shows the gusset plates 43 and 44 for this connection. The lugs 43a and 4411. are soldered to the spars 4 and the bodies of the plates are soldered to the frame members 6 and the diagonals 4|. The lugs 43a and 44a permit centric connection of all members to the spars, as shown in Fig. 15.

Referring to Fig. 6, the spars 4 are replaced by 17, and the sections are inserted in, and soldered to, notches 39 of annular spars 6. The

covering 40 is soldered to the. flanges 31 of the sections and the covering thus partakes in force transmission.

The covering is adapted to portions of irregular form, for instance,- to the roots of the wings, by folding or by wrapping. Fig. 7 shows a folded portion whose position is indicated at f in Fig. 1. A strip l3 of sheet metal is folded or pleated at H. The overlap of the folded portions increases in depth from the point of largest radius, at l5, to that of smallest radius, at IS. The folded portions are soldered at their overlapped parts. It may occur that the sheet metal cracks or is notched when the folds are formed but this can be avoided by pulling the sheet metal and is quite harmless as the cracks or notches are filled in with solder. The sheet metal may even be incised on purpose.

A wrapped portion is shown in Fig. 8, as positioned at g in Fig. 1. This portion is built up of strips l1 and I8 in intersecting arrangement as required by the curvature, and soldered together at the points of intersection. The strips l1 and I8 have been shown in spaced relation for the sake of clearness but it is understood that in fact they are in closely adjacent position.

The folded or wrapped portions are preferably ,bent to shape on suitable jigs or templates of wood or metal.

Referring now to Figs. 9a to 9f, the strips of covering, for instance, at h in Fig. 1, may be connected by joints of various kinds. In Figs. 9a and 9b, a plain overlapped joint for the strips 1 is shown. The joint illustrated in Figs. 9c and 911, is provided with a one-sided strap, and the joint illustrated in Figs. 9c and 9 has a pair of straps 8 and 9.

Obviously, I may provide any kind of overlap or strapped butt joints, as shown. The efliciency of the joint is determined by the width of the overlap, or of the straps. Fig. 10 shows two overlapped pieces of sheet metal '1, l, and, on a magnified scale, the bending moments to resulting from the forces P. At the joint I2, normal stresses occur which, if the overlap is too short, cause the soldered joint to break, beginning at the edges in where the stress is a maximum. In conformity with my invention, the overlap should be as large as practicable so that the sheet metal pieces are yielding to a sufiicient extent for keeping low the normal stresses, and only shearing stress is exerted on the soldered joint.

The several braces, struts, etc., for instance, the braces 29 on the spars and the struts 2i on the ribs, may be arranged at any angle instead of being vertical, and may be of any desired section. For instance, the sections 36 in Fig. 1'1 may be used which, when soldered to a plate or channels to the covering, make up a closed section therewith. It is not necessary that the various members, such as the spars, the rib frames, struts, etc., should consist of a single part as shown but they may be built up, and built-up sections will now be described with reference to Figs. 19 to 25. If desired, such sections may be equipped with braces, flanges and the like, not shown.

The section in Fig. 19 comprises four strips 45 which at the corners of the square section are connected by soldered angle sections 46. In Fig. 20, the strips are bent over at one side at right angles and the adjacent strip 45 is soldered to the corresponding angle 46. In Fig. 21, the sides of a section as shown in Fig. 19 are provided with crozes 41 for bracing them. In Fig. 22 channels 48 are soldered to the irmer faces of the strips 45 with their flanges 49 which project outwardly, and in Fig. 23 a similar section is shown whose have inwardly projecting flanges. Angle-section braces are shown in Fig. 24. An extra bracing is obtained in a very simple manner in the section Fig. 25, by soldering together four flanged angle sections. The various sections are made in a continuous operation by drawing strips through a folding machine and soldering the folded strips at the joints. Obviously, I am not limited to the square sections illustrated.

It will be understood that my invention relates not only to the formation of the covering from soldered pieces of thin, high-quality treated sheet metal, preferably steel, but also to the soldering of connections at the spars, ribs, frames, etc.. of the wing and fuselage structure, and of other partsv of similar metal. The several members of the structure may be varied, and such variations are indicated at a, b, and c in one of the wings, and at d and e in the fuselage.

This application is a continuation in part of my application filed Oct. 27th, 1932, Ser. No. 639,908.

What I claim is:

1. A joint structure for aircraft construction comprising lapped sheets of steel joined by a soft solder only and exposed principally to shear, said sheets being of foil-like thickness and composed of high tensile strength heat treated steel,

and said solder being fusible at a temperature intermediate the fusing temperatures of lead-tin and brazing solders for steel.

2. A joint structure for aircraft construction as in claim 1 in which the thickness of the metal sheets is of the order of .02 millimeter.

3. A Joint structure for a curved surface in aircraft construction comprising intersecting and overlapping strips of sheet metal covering said curved surface and joined by a soft solder only. and exposed principally to shear, said metal strips being of foil-like thickness and being composed of a high tensile strength heat treated steel, and said solder having a fusing temperature intermediate the fusing temperatures of lead-tin and brazing solders for steel.

ADOLF BAMBRAUS. 

